Hack saw



0 Silicon i reamed Feb, l, 1927.

nowAnn M. GERMAN,

fiTATE Lei ears eer e or GRAFTON, rnnnsYLvAmA, ASSIGNOR ro UNIVERSAL STEEL COMPANY, OF BRIDGEVILLE, PENNSYLVANIA, A CORPORATION OF PENN- SYLVANIA.

'HAcK sAw.

No Drawing.

Carbon 1.00 to 1.40 Manganese .20 to .40 .10 to .30 Sulphur .02 maximum Phosphorus .02 maximum Tungsten 1.00 to 2.00

Chromium .00 to .25

The steel is rolled into sheets of varying thicknesses from the ingots or billets. The

sheets after finishing on a sheet mill are floor annealed by, reheating to temperasteel and drawn out into elongated shape or.

lines by the rolling of the sheets. The particles of cementite are too fine to have any useful or appreciable action as abrasive grains in the steel. The cementite lines cause planes of Weakness and brittleness in the steel which are not materially changed or altered by the annealing and hardening treatment ordinarily practiced.

The hacksaws as fabricated from the sheets are then hardened. It has been the aim in the hardening of hacksaws to produce as uniform a structure as possible, it being the belief that the more uniform structure would give the best cutting results. The hardening has, therefore, beencarried out by heating the saw blades to a temperature well above the critical point, and holding for a time sufficient to not only convert the sorbite into Application filed April 19, 1926. Serial No. 103,148.

martensitaand austenite, but also to take the cementite into solution and then quickly quenching in oil. After hardening, the

' blades are tempered to produce a structure of martensite with varying amounts of troostite and sorbite; The resultant steel in the finished hacksaw blade has, therefore, been almost Wholly martensite with varying amounts of-troostite and sorbite, and little or no free cementite.

with i I have discovered that the cutting and wearing qualities of hacksaws may be greatly improved by having free cementite 1n the form of nodules in the finished hacksaw. The metallog'raphic sructure of the finished hacksaw consists of'hard abrasive particles of cementite embedded in a softer and tougher matrix, usually martensite with varying amounts of troostite and sorbite. As is well known, the cementite or free carbide is very hard, in fact, being the hardest constituent of steel.

The advantages of having the steel structure containing the hard cementite nodules will be apparent from consideration of the action of the hacksaw in cutting. When the hacksaw first starts to cut, the sharp cutting points of the teeth remove a curled chip somewhat similar to the action of a lathe 7 tool. After the hacksaw teeth become dull and slightly rounded, curled chips are no longer produced. ting saws and tools, the teeth of a hacksaw dull, but the saw is allowed to operate until it is worn out. After the teeth become dull so as to no longer be capable of cutting curled chips, a considerableportion of the erty of the steel. A

I have found that the hard nodules of ce-- mentite in my improved hacksaw give the hacksaw a much greater abrasive. property than hacksaw blades having the usual uniform-metal structure. As a result, 'Iny hacksaw blades have been found to do from to 300% more work than the usual hacksaws. In addition to cutting considerably bettenthe-matrix or bond of my hacksaws is decidedly tougher, and the saws are less liable to break.

By'the process of heat treatment herein- Unlike other metal cut-x are not ground or sharpened on becoming cutting is dependent upon the abrasive prop- I after described, I have been able to utilize the ordinary hacksaw steel of a composition described above, although I prefer to vary this composition somewhat by increasing its. tungsten and chromium content.

The process will first be described in connection with the usual hacksaw steel, the

analysis of which is described above.

After the sheets are finished on a sheet mill in the usual way, they are given a spe-. cial annealing treatment, which causes the cementite to coalesce into the desired abrasive nodules instead of being uniformly distributed in the patches or lines as in the usual annealing treatment.

.My s ecial annealing treatment consists in packing the steelsheets in an annealing box to exclude air and furnace gases, and hea'tin to a temperature slightly underthe critica point, and then slowly cooling. With the usual hacksaw steels, the annealing temperature is-about 1350 to 1375 F. The

sheets are heated at this temperature for about eighteen hours and are then allowed to slowly cool in the furnace, as is the usual ractice in annealing, for about thirty hours. his special annealing at the higher annealing temperatures causes the free cementite to holding the embedded nodules of cementite.

be converted from its more or less uniform patch or line-like distribution, into small nodules or spheroids of a size to serve as abrasive grains in the finished saw. The structure of the steel afterannealing is principally sorbite, with probably small amounts of pearlite in the form of a matrix The annealed sheets are then subjected to the usual shearing, milling and setting operations to form the hacksaw blades.

The blades are then hardened. My hardening treatment differs radically from that now employed in that instead of heat treating to form a uniform .martensitic-austenitic structure,- a non-uniform or heterogeneous structure is formed b preserving the cementite in its nodular orm produced during the'annealing operation. The hardening is accomplished by heatingv the hacksaw blades to ]llSt over the critical point, usually about to 100 F. above the critical point, and,

'. quenching.

a a toug er saw blade, changes some of the The blades are brought up to this temperature and held there for two or three minutes,

and then immediately quenched in oil. The temperature and time of heating should be such as totake the sorbitic matrix into solution, but without dissolving any appreciable amounts of the nodular cementite. 'The' steel after quenching, consists of a ground massor matrix. of martensite with a considerable amount of free cementite in the form of nodules or grains disseminatedthrough the-matrix.

Tem ering, which is alsodone to produce combination with the iron carbide.

inartensite to troostite and sorbite, but does not alter the cementite nodules which have I been preserved through ment. I

While hacksaw blades having improved cutting and wearing (prialities may be pro duced by my process om the present day standard hacksaw steel, I have found that still better hacksaw blades may be produced by varying the standard composition somewhat and treating it by the same process as that described above. In modifying standard hacksaw steel formula, I increase the tungsten and chromium because the tungsten and chromium increases the quantity of the the hardening treathard segregated cementite nodules in thefinished saws.

The preferred composition of the steel is carbon .90 to 1.50%, preferably 1.10 to 1. 10%, tungsten preferably 2.00 to 5%, but

not over about 7%, chromium preferably .50 to 2.50% but-not over about 3%, and manganese, silicon, sulphur and phosphorus within the usual ranges of crucible and tool steels,

the manganese being preferably .20 to .50%,

silicon preferably .15 to 30%, and the sulphur and phosphorus preferably not over about 04% each. This steel can be made and rolled about the same as the usual standard present day hacksaw steel. Its chromium,

and particularly its tungsten content, is

tempering of the matrix by the frictional heat generated in cutting. V I In describin the hard carbide or carbldes forming the a r'asive nodules, I have described them as cementite, using theterin as 3 one of general definition and not of l1m1tation, and all to include'not only the pure iron carbide, but also the impure cementite containing tungsten and chromium carbides m Such free cementite is often referred to as carbides" or free carbides.

While I have specifically described the preferred embodiment of my inventiomit is to be-understood that the invention 15 not so limited, but may be otherwise embodied within the scope of my claims.

I claim--- 1. A hardened steel hacksaw blade con-.

raining embedded nodules of coalesced cementite of a size sufiicient to serve as abrasive grains.

2. A hardened steel hacksaw blade containing tungsten not over about 7%, andcontaining embedded nodules of cementite of a size sufficient to serve as abrasive grains.

3; A hardened steel hacksaw blade containing between .about 1% to 7% tungsten and chromium not over about 3% and containing embedded abrasive nodules of ce mentite;

at. A hardened steel hacksaw blade containing about 2% to 5% tungsten and about .5% to 2.5% chromium and containing embedded abras-ive nodules of, cementite.

5. A hardened steel hacksaw blade containing tungsten not over about 7% and having a metal structure characterized by free cementite segregated in nodular form in a matrix of softer metal, said nodules of cementite being of a size sufficient to serve as abrasive grains.

6. As an intermediate product in the manufacture of steel hack saw blades, an annealed steel sheet containing embedded abrasive nodules of cementite.

7. As an intermediate product in the manufacture of steel hacksaw blades, an annealed steel sheet containing tungsten not over about 7%, and containing embedded abrasive nodules of cementite.

8. As an intermediate product in the manufacture of steel hacksaw blades, an annealed steel sheet containing between about 1% and 7% tungsten, and chromium not over about 3%, and containing embedded abrasive nodules of cementite. I

9. As an intermediate product in the man utacture of steel hacksaw blades, an annealed steel sheet containing about 2% to 3% tungsten and about 5% to 2.5% chromium, and containing embedded abrasive nodules of cementite. s

10. The process of hardening hacksaw blades of steel containing abrasive nodules of cementite, which comprises heating them to a temperature and for a time sufiieient to cause the steel matrix to go into solution but insufficient to permit the dissolution of appreciable amounts of the cementite nodules, and quenching.

11. The process of hardening hack-saw blades of steel containing embedded abrasive nodules of free cementite, Which comprises heating them to a temperature of just over the critical point for a time insufiicient to cause the cementite nodules to go into solution and quenching.

12. The process of making steel hacksaws which comprises forming into sheets a hacksaw steel containing free cementite, annealing the sheets so as to cause the cementite to coalesce into nodules, fabricating hacksaw blades from the sheets, and hardening the blades by heating them to a hardening temperature and for a time insufficient to break up the cementite nodules, and quenching.

13. The process of making steel hacksaws which comprises making a hacksaw steel containing tungsten not' overabout 7% and chromium not over about'3% and characterized by the presence of free cementite, forming the steel into sheets, annealing the sheets by heating to a temperature below that atwhich the cementite goes into solution but sufiicieiit to cause the cementite to coalesce,

into nodules, fabricating hacksaw blades from the annealed sheets, and hardening the blades by heating to a temperature and for a time sufiicient to cause hardening after quenching but insuflicient to cause the cementite nodules to go into solution to a substantial extent, and quenching.

In testimony whereof I-have hereunto set my hand. i

HOWARD M. GERMAN. 

